The broke brakes combination

[GPster]

I bought a '80 CJ7 Jeep so maybe I could work on something and enjoy a sense of accomplishment. I haven't gotten there yet. This thing has been mudded and when I inspected it (after I bought it, dumb) I found a brake line to the rear broken. Because it stopped and there was plenty of fluid in the master cylinder I was pleased that the combination valve had done it's job. I went about the business repairing the line. While it was up on jack stands I placed the new line to lessen some of the stress that the "Lift" had created. I fixed a broken shock mount and snaked some of the dirt from inside the frame rails. I tried to bleed the rear brakes and got nothing. Tried to vacuum bleed the brakes and still nothing. Checked some Jeep sites and they all pointed at that combination valve with comments from they will reset themselves when the problem is corrected, use a "C" clamp to depress the plunger, use needle nose pliers to pull the plunger out and "I've never had a problem". A Jeep service book shows some AMC tools used on the valve to prevent the problem but the pictures show what the tool looks like, not what it does. With all of this information and no answer I decided to do something I thought I could accomplish so I pulled the rear drums to inspect the brake shoes. This thing hasn't had working rear brakes for a long time. And they knew it. the self adjusters were gone, the parking brake mechanism was gone and everything that was left was packed in mud. I figured that the wheel cylinders were probably not repairable so I ordered some new ones. While waiting on parts I thought maybe getting fluid in the new lines might help the condition. I sucked fluid through the line from the combination valve to the wheel cylinders and was surprised how clean the fluid came through. So I tried to bleed the brakes again and still could get no fluid through that combination valve to the rear. Back to the Jeep sites and someone had made the statement that if the combination valve had spent a lot of time being off centered it probably would be stuck that way and would need replaced.  There are five lines to the combination valve. I broke the line to the rear at the nut and my faith in getting the other four lines unhooked and whole is slim. Any tips on resetting those valves that might work? There is a kit that uses a GM combination valve and mounts it up and along side the master cylinder. It would require new lines too but at least it wouldn't be in the 3" space between the frame rail and exhaust pipe. I just wrote this novel to take the strain off of Wayne. Now you are all free to read about the 20 year old that won the Daytona 500. GPster

[wayne petty]

to get the switch to recenter..  you have to bleed the front brakes...

i have run into a few that were really hard to recenter after being stuck a while...

i have had to loosen the line into the half that supplies the rear brakes into the combo valve..  to get it to bleed from the master to the combo valve..

after doing that.. then i can loosen the one of the front lines.. and stand on the brakes... this will usually slam the valve shuttle forward...


inside the valves.. are nothing usually but the valve with Orings ...

i don't know .. yep...  what type of Oring will survive brake fluid.. you can do a test...  just replace the orings...

i have also taken the switch from the side...  so i could see the shuttle. then probed and worked it over... carefully...  with a probe.. not something you really want to do...

are you sure that some jack.. .....  did not install a nail in the brake lines to prevent fluid loss...  i have found that also..

i think pirate jack brakes has a great selection of combo valves...


oh.. and when i am bleeding brakes... with a line loose.. i have found that just tapping the pedal... so you build a little pressure without covering the fill ports.. this pushes fluid without creating vacuum to pull air back in the system....


i saw them hold up the bio for the driver.... its short...  line one... wins daytona 500 2011....  

[Charlie Chops 1940]

Joe,

The last time I ran across this problem was with a long term (almost 200K) '79 Riviera front disc/rear drum car. The first brake job I did caused the combination valve to shuttle and cover the exit for the rear brakes. I solved it by removing the brake warning switch from the top center and scribing a mark in the piston then prying it back with the scribe tool until I couldn't see the mark. Then I put the switch back in and gravity bled the rear brakes until I got clean fluid. Then I pressure bled the whole system.

I did that same drill for three brake jobs as I kept forgetting that the piston would shuttle with the "normal" pump and crack the wheel cylinder method.

I've never had any other combo valve do that.

Charlie

[UGLY OLDS]

I still have a little knurled tool that is threaded with a small pin we used to use on Ford trucks .. The shuttle valves on those were very sensitive & would "crossover" during bleeding keeping the brake warning light on ..

The idea with the little tool was to remove the warning light switch BEFORE any brake repairs were attempted .. Screw in the little tool...It would lock the shuttle in place so it could not move .. When the repairs were completed, you removed the tool & re-installed the warning light switch ... I too have "Re-centered" many of them with a pick .....


Bob..

[GPster]

are you sure that some jack.. .....  did not install a nail in the brake lines to prevent fluid loss...  

That tip hit the NAIL on the head. I think that maybe that mechanic had perfected that procedure though. When I removed the line for the rear brake circuit from the master cylinder I found a fillister head phillips screw screw in the line. It was probably a size 10 screw because the screw shank fit close in the ID of the 1/4" line. Everything worked after it's removal. Now to proceed finding things wrong. Thanks, I'll put all of the suggestions in my memory bank. GPster